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From: Peter Zijlstra <peterz@infradead.org>
To: Sean Christopherson <seanjc@google.com>
Cc: kernel test robot <oliver.sang@intel.com>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>,
	x86@kernel.org, lkp@lists.01.org, lkp@intel.com
Subject: Re: [x86/entry_32]  aa93e2ad74: BUG:soft_lockup-CPU##stuck_for#s![systemd-logind:#]
Date: Wed, 12 Jan 2022 11:25:53 +0100	[thread overview]
Message-ID: <Yd6ssarpDknV1r9z@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <Yd4u2rVVSdpEpwwM@google.com>

On Wed, Jan 12, 2022 at 01:28:58AM +0000, Sean Christopherson wrote:
> On Tue, Jan 11, 2022, Peter Zijlstra wrote:
> > On Thu, Jan 06, 2022 at 04:35:23PM +0800, kernel test robot wrote:
> > > 
> > > 
> > > Greeting,
> > > 
> > > FYI, we noticed the following commit (built with clang-14):
> > > 
> > > commit: aa93e2ad7464ffb90155a5ffdde963816f86d5dc ("x86/entry_32: Remove .fixup usage")
> > > https://git.kernel.org/cgit/linux/kernel/git/tip/tip.git x86/core
> > > 
> > > in testcase: kernel-selftests
> > > version: 
> > > with following parameters:
> > > 
> > > 	group: x86
> > > 
> > 
> > It would be very useful if this thing would also say which of the many
> > x86 selftests fails... it appears to be: ldt_gdt_32.
> > 
> > The below fixes it, but I'm still not entirely sure what the actual
> > problem is, although Andy did find a bug in that the exception handler
> > should do: *(ss:esp) = 0, adding ss-base (using insn_get_seg_base())
> > doesn't seem to cure things.
> 
> Because I was curious...
> 
> The issue is that PARANOID_EXIT_TO_KERNEL_MODE in the handle_exception_return
> path overwrites the entry stack data with the task stack data, restoring the "bad"
> segment value.

Oh gawd... that's terrible, and yes, that now makes perfect sense.

However did you find that?

WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: lkp@lists.01.org
Subject: Re: [x86/entry_32] aa93e2ad74: BUG:soft_lockup-CPU##stuck_for#s![systemd-logind:#]
Date: Wed, 12 Jan 2022 11:25:53 +0100	[thread overview]
Message-ID: <Yd6ssarpDknV1r9z@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <Yd4u2rVVSdpEpwwM@google.com>

[-- Attachment #1: Type: text/plain, Size: 1325 bytes --]

On Wed, Jan 12, 2022 at 01:28:58AM +0000, Sean Christopherson wrote:
> On Tue, Jan 11, 2022, Peter Zijlstra wrote:
> > On Thu, Jan 06, 2022 at 04:35:23PM +0800, kernel test robot wrote:
> > > 
> > > 
> > > Greeting,
> > > 
> > > FYI, we noticed the following commit (built with clang-14):
> > > 
> > > commit: aa93e2ad7464ffb90155a5ffdde963816f86d5dc ("x86/entry_32: Remove .fixup usage")
> > > https://git.kernel.org/cgit/linux/kernel/git/tip/tip.git x86/core
> > > 
> > > in testcase: kernel-selftests
> > > version: 
> > > with following parameters:
> > > 
> > > 	group: x86
> > > 
> > 
> > It would be very useful if this thing would also say which of the many
> > x86 selftests fails... it appears to be: ldt_gdt_32.
> > 
> > The below fixes it, but I'm still not entirely sure what the actual
> > problem is, although Andy did find a bug in that the exception handler
> > should do: *(ss:esp) = 0, adding ss-base (using insn_get_seg_base())
> > doesn't seem to cure things.
> 
> Because I was curious...
> 
> The issue is that PARANOID_EXIT_TO_KERNEL_MODE in the handle_exception_return
> path overwrites the entry stack data with the task stack data, restoring the "bad"
> segment value.

Oh gawd... that's terrible, and yes, that now makes perfect sense.

However did you find that?

  reply	other threads:[~2022-01-12 10:26 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-06  8:35 [x86/entry_32] aa93e2ad74: BUG:soft_lockup-CPU##stuck_for#s![systemd-logind:#] kernel test robot
2022-01-06  8:35 ` kernel test robot
2022-01-11 11:11 ` Peter Zijlstra
2022-01-11 11:11   ` Peter Zijlstra
2022-01-12  1:28   ` Sean Christopherson
2022-01-12  1:28     ` Sean Christopherson
2022-01-12 10:25     ` Peter Zijlstra [this message]
2022-01-12 10:25       ` Peter Zijlstra
2022-01-12 16:14       ` Sean Christopherson
2022-01-12 16:14         ` Sean Christopherson
2022-01-12 10:55     ` [PATCH] x86/entry_32: Fix segment exceptions Peter Zijlstra
2022-01-12 10:55       ` Peter Zijlstra
2022-01-12 15:42       ` Borislav Petkov
2022-01-12 15:42         ` Borislav Petkov
2022-01-13 18:54         ` Andy Lutomirski
2022-01-13 18:54           ` Andy Lutomirski
2022-01-13 19:55           ` Peter Zijlstra
2022-01-13 19:55             ` Peter Zijlstra
2022-01-14 11:24             ` Borislav Petkov
2022-01-14 11:24               ` Borislav Petkov
2022-01-14 23:48               ` Andy Lutomirski
2022-01-14 23:48                 ` Andy Lutomirski
2022-01-15  8:13                 ` Borislav Petkov
2022-01-15  8:13                   ` Borislav Petkov

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